docs: def _delete_at(self, timestamp, using=None):
          """
          WARNING: This method is only for internal use, it should not be used
          from outside.
  
          It is used only in the case when you want to make sure a group of
          related objects are deleted at the exact same time.
  
          It is certainly not meant to be used for deleting an object and giving
          it a random deletion date of your liking.
          """
          if self.version_end_date is None:
              self.version_end_date = timestamp
              self.save(force_update=True, using=using)
          else:
              raise DeletionOfNonCurrentVersionError(
                  'Cannot delete anything else but the current version')